This invention relates to a pressure sensitive sealant composition and a method for sealing by using the sealant composition, and more particularly to the sealant composition which is used in a clearance between a rear combination lamp unit and a vehicle body of an automotive vehicle and provided with improved watertight seal under environmental condition where the vehicle is used, improved operational efficiency for repairing and disassembly of the lamp unit, and improved removal characteristics allowing the sealant composition to be peeled of in an interfacial breaking condition, and the sealing method by use the sealant composition.
In an assembly process of a modern automotive vehicle, lamp (light) unite such as rear combination lamp units are installed to a vehicle body which has been painted, at a trimming step. At this time, a variety of sealing materials are used in a clearance between each lamp unit and the vehicle body for the purpose of obtaining water-tight seal therebetween. In general, a molded gasket or a butyl rubber based adhesive is used as the sealing material The molded gasket is usually formed by punching out a sheet formed of closed cell-type foam rubber or plastic, and the butyl rubber based adhesive is usually applied upon heating at a temperature not lower than 100xc2x0 C.
Concerning the molded gasket, it has been previously formed by punching out the above sheet into a shape corresponding to a portion requiring a water-tight seal on the side of a housing of the rear combination lamp unit. The thus formed molded gasket is assembled in the seal required portion on the side of the rear combination lamp unit housing. This molded gasket exhibits its water-tight seal under the effect of resilience generated upon compression or when compressingly put between the rear combination lamp unit housing and the vehicle body panel by engaging small screws provided on the side of the rear combination lamp unit housing. More specifically, the molded gasket is usually formed by punching out the sheet of the closed cell-type foam material by using a metallic die or a so called Thomson blade. The foam material is made of rubber (such as EPDM=copolymer of ethylene, propylene and diene), polyurethane resin, silicone resin or the like, and has been foamed to have a volume of 3 to 5 times that in its not-foamed state. In such a case, the molded gasket is used upon being compressed 25 to 50% in direction of thickness thereof when the rear combination lamp unit is assembled in the vehicle body, in order to obtain necessary resilience for the purpose of securing a water-tight seal between the rear combination lamp unit housing and the vehicle body panel.
However, under environmental conditions where automotive vehicles are used, the above molded gasket employed in a compressed state will be subjected to permanent deformation due to its deterioration caused by heat and/or humidity upon long time use. This relatively lowers the resilience of the molded gasket and therefore degrades water-tight seal. With this, water penetrates into, for example, a trunk compartment of the vehicle. Furthermore, such a molded gasket is not necessarily sufficient in follow-up characteristics to polyvinyl chloride-based sealant applied at a plurality of step sections having a step-height of about 1 mm in the vehicle body panel, for example, at a so-called zero joggle joint section between a rear fender panel and a rear panel, each section requiring water-tight seal. When the rear combination lamp unit is assembled in the vehicle body having such a surface structure, water-tight seal between the rear combination lamp unit and the vehicle body becomes insufficient thereby causing, for example, water leak into the trunk compartment of the vehicle.
Concerning the butyl rubber-based adhesive, it is first heated at a temperature of not lower than 100xc2x0 C., and then applied on the surface of the housing of the rear combination lamp unit, following the shape of a section requiring watertight seal. Such a butyl rubber-based adhesive can exhibit water-tight seal between the rear combination lamp unit and the vehicle body under a high adhesiveness to the plastic surface of the rear combination lamp unit housing and to the painted surface of the vehicle body panel, not under resilience generated upon compression as in the molded gasket. Besides, the butyl rubber-based adhesive is usually applied at the temperature of not lower than 100xc2x0 C. along the shape of a groove formed on the surface of the tear combination lamp unit housing in such a manner as to take the state of a bead having a cross-sectional diameter ranging from 8 to 12 mm. Thus, the butyl rubber-based adhesive can provide water-tight seal in an interfacial region between the rear combination lamp unit housing and the vehicle body panel under the action of the high adhesiveness against the surface of the lamp unit housing and the surface of the vehicle body panel.
In general, the butyl rubber-based adhesive has such a characteristic that stress can be reduced immediately after compression and therefore it does not have resilience. Accordingly the butyl rubber-based adhesive does not make its decomposition and permanent deformation in the direction of thickness, owing to its deterioration upon being subjected to heat and humidity for a long time in the environmental conditions where automotive vehicles are used. Additionally, the butyl rubber-based adhesive can be smoothly reduced in stress immediately after compression, and therefore is sufficient in follow-up characteristics to step sections having a step-height of around 1 mm in the vehicle body panel at a section requiring water-tight seal. Thus, the butyl rubber-based adhesive is not problematic from the viewpoint of reliability for water-tight seal.
However, the butyl rubber-based adhesive is high in adhesiveness, and therefore a edge section of the rear combination lamp unit is required to be broken open by a plastic bar or the like while it is gradually heated by an industrial dryer or the like, for the purpose of disassembling the rear combination lamp unit when the rear combination lamp unit is replaced with a new one in an automotive vehicle service factory or the like. Such operations are very troublesome. Additionally, when the rear combination lamp unit is disassembled, the butyl rubber-based adhesive make its breaking (cohesive breaking) while leasing remains of the butyl rubber-based adhesive on the both surfaces of the vehicle body panel and of the rear combination lamp unit housing. Accordingly, in case that the new rear combination lamp unit with new butyl rubber-based adhesive is re-assembled in the vehicle body, it is required to manually remove the remains of the adhesive containing a large amount of dust, dirt and oil, left on the surface of the vehicle body panel, in order to secure water-tight seal after re-assembly of the new rear combination lamp unit. Such operations require a long time and a considerable labor. Besides, there is the fear that the butyl rubber-based adhesive adhered to the hands of an operator again adheres onto the painted surface of the vehicle body and to interior trims of the vehicle, thereby degrading the external appearance of the vehicle after the displacement operations for the rear combination lamp unit.
Further, when the vehicle is dismantled or scrapped, it is substantially impossible to recover and recycle the plastic materials (mainly polypropylene resin) of the rear combination lamp unit housing because it is very difficult to remove the butyl rubber-based adhesive which has been adhered deeply to the bottom surface of the grove formed on the rear combination lamp unit housing.
In view of the above drawbacks encountered in conventional techniques, the inventors have conducted researches and developments and found that a pressure sensitive sealant composition having a particular composition can effectively solve the conventional drawbacks, thereby reaching the present invention.
It is an object of the present invention to provide an improved pressure sensitive sealant composition and an improved sealing method, which can provide excellent water-tight while allowing the pressure sensitive sealant composition to be easily removable from a base member to which the sealant composition has been applied.
Another object of the present invention is to provide an improved pressure sensitive sealant composition and an improved sealing method, which can be effectively used in and for a clearance between a rear combination lamp unit and a vehicle body panel of an automotive vehicle, thereby exhibiting excellent water-tight seal and high operational efficiency for repairing and disassembly of the lamp unit, while preventing remains of the pressure sensitive sealant composition from being left on the surfaces of the rear combination lamp unit housing and the vehicle body panel.
An aspect of the present invention resides in a pressure sensitive sealant composition which comprises (a) 10-40 wt % of a component A that is at least one copolymer selected from the group consisting of hydrogenated styrene-butadiene copolymers, hydrogenated styrene-isoprene copolymers, and modified copolymers thereof; (b) a component B that is at least one tackifier selected from the group consisting of petroleum resins, terpene resins, rosin resins, coumarone-indene resins, hydrogenated resins thereof, and modified resins thereof: and (c) a component C that is a hydrocarbonic plasticizer, wherein said pressure sensitive sealant composition is prepared by mixing together 100 parts by weight of said component A, 20-60 parts by weight of said component B, and 150-400 parts by weight of said component C.
Another aspect of the present invention resides in a method for sealing a member, which comprises (a) preparing the pressure sensitive sealant composition; (b) heating the pressure sensitive sealant composition; and (c) applying the heated pressure sensitive sealant composition to the member.
A further aspect of the present invention resides in a method for sealing a member, which comprises (a) preparing the pressure sensitive sealant composition; (b) forming the pressure sensitive sealant composition into a predetermined shape; and (c) applying the pressure sensitive sealant composition of the predetermined shape to the member.